1. Field of the Invention
The present invention relates to a fuel cutoff valve mounted on an upper wall of a fuel tank to open and close a connection conduit, which connects the inside of the fuel tank with the outside.
2. Description of the Related Art
Conventional fuel cutoff valves have been known in JP-A-2004-308838, and JU-A-5-1547. The fuel cutoff valve is mounted on the upper wall of a fuel tank, and comprises a casing with a connection conduit that connects to the outside (the canister) and a float that rises and falls with changes in the buoyant force according to the fuel level within a valve chamber of the casing. The fuel cutoff valve closes the connection conduit by the float rising due to an increase in buoyant force due to an increase in the fuel level within the fuel tank, preventing the fuel from flowing to the outside.
The conventional fuel cutoff valve float is formed with a thin-wall cup shape providing a buoyancy chamber, open towards the bottom, which prevents the occurrence of shrinkage that tend to occur at the time of the injection molding of the float, making it possible to increase the precision of the molding. In this type of cup-shaped float, the buoyancy chamber is sealed off when the fuel level rises above the bottom edge of the float. The vapor in the sealed buoyancy chamber expands and contracts depending on changes in the temperature within the fuel tank, causing variability in the buoyancy of the float. Because of this, the fuel cutoff valve has a problem in that the cutoff fuel level will vary depending on changes in temperature within the fuel tank. When the buoyancy chamber is reduced in size in order to solve this problem, then not only does the molding precision of the float suffer due to shrinkage in the resin at the time of injection molding, but there is an additional problem in that this also causes a reduction in productivity due to the increased time required for cooling.